How often should you need to top up the water in a closed boiler system?

[Wiifitmama]

We woke to no heating or hot water. Checked the boiler and the error message about the pressure being too low was on there. Dutifully topped up and now all fine. But we did top it up in the last 5 or 6 months if I am remembering correctly. IS this normal - sort of twice a year? And why? Where is the water going? Or is it an indication of a problem? Where should we check?

It's leaking. The leak(s) might be so tiny that you don't notice them and the water dries up (especially on a hot component). Or there is a chance the pressure relief valve is dripping (look at the small copper pipe going through the wall outside your house, and bent round to point at the outside wall) and should be replaced.

You may find limescale or green stain showing where it is. I like to polish up copper pipes with a green kitchen scourer so any new marks become obvious, but you may think that obsessive. The first green stains are from plumbers flux, but any subsequent ones are leaks.

Have a look round the radiator valves, including the bleeding vents, first, and in the airing cupboard if you have one.

Plumbers will tell you that leaks heal themselves in time. This means they clog up with limescale.

Topping up once or twice a year is normal, but it will dilute the corrosion inhibitor, so maybe add some every five years.

I had to sort my boiler pressure out last week - dropped because I'd bled the radiators. I watched a YouTube video to learn how to do it and I think he said you have to do it every six months or so.

Hmmm, ok thanks. We have guests about to arrive so will check after they leave. We had the boiler moved (and serviced) about a year or so ago with a big extension and refurb project. I am not sure if this makes it more or less likely to be a leak!!

More.

Every joint has a possibility of leaking, so if you put in another 50 new joints, the probability increases.

Plumbers will tell your their joints never leak.

@PigletJohn : What type of corrosion inhibitor and where do you put it?

The same type that the installer used. There will (should) be a label on of near the boiler or cylinder or a note in the installation paperwork.

Sentinel and Fernox are very popular but there are some budget brands.

With a sealed system it is often injected into the system filter (if any) or a radiator bleed plug. Although you can learn to DIY it might be easier to get the maintenance person to do it. If you DIY the best time is when the pressure has dropped, before topping it up.

Open-vented systems with a small expansion tank in the loft are easier, but considered old-fashioned.

Thanks. So dh went outside to look where the pipe comes out. He said where there is a joint in the plastic pipe (it bends and goes down to a drain), there is water dripping.

I have no idea what this means though!

different thing. The plastic pipe is condensate from the boiler flue. The leak needs to be fixed, anyone who can do plumbing can fix it. Maybe add some armaflex lagging if there is a risk the pipe could freeze. Usually the plastic pipe is solvent welded, and has a brand name printed on the side so you can buy a connector to fit. Condensate is acidic and slowly erodes concrete, mortar and limestone.

A condensate leak won't drop the pressure in the boiler.

Ah interesting thanks. That makes sense. Last winter that plastic pipe froze and we had to pull it apart (wit plumber) to get the ice out so the boiler would work again. We just shoved the pieces back on after so I assume that is why there is a leak at the joint now - we never sealed it or anything.

Hmmmm....so it is not that, which means there is a leak somewhere. I will look inside the boiler cupboard itself. It is a mess of pipes!! We had underfloor heating put into two new extensions which extended the whole system.

Armaflex make a black, rubbery pipe insulation which is more durable than the plastic foam mostly used for indoor work. It's more expensive but you won't need much.

It could also be due to a failing expansion vessel in the boiler - I’d get it looked at soon because I kept topping ours up and this caused another part to fail, which turned the repair into a £400 job when it would have been £200.

good point, but that would start making the pressure changes between hot and cold increasingly dramatic.

Does that mean that the gauge where it shows the green and red zones with numbers? So when the boiler is on, I see that moves higher sometimes. Is that what you are talking about by dramatic pressure changes? What should I see?

it should be in the green, hot or cold.

I expect yours is mostly somewhere around 1.5

It will move somewhat up and down when hot and cold, if the expansion vessel is not able to absorb as much of the expansion as it did when new, it will move noticeably further. Eventually, it will expand into the red, and eventually, it will vent out overpressure through the copper pipe through the wall I mentioned earlier. Once it has vented through the valve, the valve will tend to drip because it may not reseal tightly.

Thanks PigletJohn - just to clarify and make sure I understand, if the pressure does fluctuate a lot, and ends up relieving by going out that pipe, that would cause the loss of water in the system presumably? So if we watch the pressure as it gets hot and cold over the next few days and see that fluctuation, we can assume we need that pressure valve replaced to stop the loss of water?

I just checked the pressure now and the boiler is on (temp around 75) and the pressure has gone up into the red at around 3. I checked it earlier and it was around 1.5 pressure (temp around 55) so I am assuming this is conclusive that it is the pressure valve that is the problem?

that's a big jump.

I think you are right (actually the expansion vessel, not the valve)

best call in a mender. They may be able to pump it up to get you through Christmas, and fit a new one afterwards.

Try to relieve pressure down to the bottom of the green section when cold. You can do this by letting water out at a radiator bleeder.

Try not to bleed air out until fixed, any air in the rads will absorb a bit of expansion.

Well spotted Hermione

You shouldn't really

I used to have a leaky boiler and it needed topping up very regularly though

p.s.

you can ask them to top up the inhibitor when the new vessel is fitted.

We had the problem you describe last year and it required a new expansion vessel. Been fine since.

Is it that urgent I need someone before Christmas? I only had to top it up once. I was assuming I could get through the holiday period and call someone in after?

it's no longer the topping up that's the problem, it's the overpressure. If you can keep it out of the red it may save the boiler from squirting hot water down the outside of the house, in which case you probably won't need a new pressure release valve. Once they have released, they tend not to seal correctly and need to be replaced. Sometimes it's possible to take them off, dismantle and clean, but that may be no cheaper than swapping for a new one.

You'll be fine to leave it till after Xmas. If it goes into the red turn the heating off and run the hot taps till the pressure lowers or bleed one of the radiators to let the pressure out.
If it gets too low, top it up.